For the vast majority of Americans, when we talk about "arms" we recognize that we are talking about a very large gradient and we all eventually fall somewhere on it. (Apologies in advance for a bit of hyperbole here). Those "arms" range from 2" pen knives to nuclear weapons. In general, people tend to draw the line somewhere involving bullets. Some are cool with the current limitations on fully automatic machine guns, others would like that repealed. Others look at magazine capacity while the opposite camps sees that as gross infringement. Some would be cool with much larger "arms" like explosives and RPGs being legalized, while a majority of Americans think that is ludicrous. I am guessing that most of us here have no problem with almost any knife we can think of as an "arm" while others freak out about silly stuff like balisongs. I think limiting knives in places like schools makes sense, others think that makes us a nanny state.
My point is that if you look at the broad definition of arms as you are suggesting we do, then there is usually a line somewhere that we can conceded. If you are a fully fledge 2A to limit means whatever weapon you can get your hands on, I am curious if your view would change if a muslim immigrant from Syria wanted to own an RPG.
Point is, guns have never been a black and white issue. It has always been grey. We aren't argueing pro or anti weapons, we are just debating on where we draw that line.